1. Field of the Invention
The present invention relates generally to air cleaning methods for capturing and treating contaminated air or emissions from mechanical industrial processes, and more particularly, to methods for cleaning contaminated air from a wet or dry mechanical industrial process, such as machining, material working or the like, which address the cloud-like behavior of contaminated air containing a heterogenous multi-component mixed density fluid (e.g., mist, vapor and/or smoke) that is generated by such a mechanical industrial process.
2. Description of Related Art
In the field of mechanical industrial processes, such as machining, metal working, material fabrication and the like, it is well known to use some type of air cleaning system to capture and treat the contaminated air and other emissions produced by the industrial process. During operation of these types of mechanical industrial processes, contaminated air containing mist, vapor, and smoke is produced, particularly whenever liquid coolants are used on, or near, the working surface of the operation. In a cutting or grinding operation, for example, liquid coolant is evaporated and thrown by the cutter or grinder into the air space surrounding the work area. Although large coolant droplets and chips of material may fall to the ground, small coolant droplets, mist and vapor and very small pieces of material and dust become suspended in the air space surrounding the work area to form a thick haze of contaminated air.
Many early air handling systems for industrial processes simply captured the contaminated air by use of a hood or other source capture mechanism, and then vented the contaminated air and other emissions directly to the outside. With the advent of air pollution regulations, these systems began to include air cleaning apparatus in an effort to remove harmful contaminates from the air stream prior to venting it to the outside. Over the years, many different types of air cleaning apparatus have been used in an effort to clean up the contaminated air and other emissions from industrial processes. Typically, contaminated air would be captured at multiple locations or work areas within a factory, for example, and then routed by ventilation duct work to a common air cleaning apparatus, often located outside the factory. A variety of different dust collection and/or mist removal apparatus, such as helical separators, cyclone separators, scrubbers, mechanical and electrical filters and the like, have been used to dean the contaminated air once it is within the air cleaning system. Examples of these type of apparatus are shown in U.S. Pat. Nos. 4,038,056, 4,216,003, 4,364,754, 4,382,807, 4,460,386, 4,350,504, 5,024,681, 5,110,331, 5,120,335, 5,129,930 and 5,178,656, as well as the Heli-Flow.RTM. system manufactured by the assignee of the present invention, the Monsanto Organic Package System manufactured by Monsanto Enviro-Chem Systems, Inc., St. Louis, Mo. and the Duct Type Mist Separator KNA manufactured by Delbag Luftfilter, Germany.
Regardless of the type of dust collection and/or mist removal apparatus used for an air cleaning system, most existing air cleaning methods attempt to remove contaminants in an air stream by treating the contaminants as discrete particles. Typically, the contaminants in the air stream from a mechanical industrial process will be either in the form of mist (small droplets of liquid suspended in the air stream), or smoke/dust (small particulates of solid suspended in the air stream), or both. As a result, the theory behind the operation of these dust collection and/or mist removal apparatus relies on some type of physical separation of the discrete particles of mist and/or smoke from the air stream. Such a physical separation can occur, for example, as a result of the direct impact of the particles with the fibers of a filter, the centrifugal force imparted to the particles by a cyclonic apparatus, or the addition of an electrostatic charge to the particles.
An increasing number of mechanical industrial processes, however, also generate a significant amount of vapor, as well as smoke and/or mist as part of the contaminated air stream. Vapor is typically generated when a liquid is used in the mechanical industrial process, such as for cooling lubricating. Due to the heat energy dissipated during the mechanical industrial process, a portion of the liquid is evaporated into a gaseous phase vapor. Unfortunately, existing dust collection and/or mist removal methods which rely on physical separation of discrete particles simply cannot handle a gaseous phase vapor as part of a contaminated air stream. Because there are no physically discrete liquid phase or solid phase particles in a gaseous phase vapor, the gaseous phase vapor component of a contaminated air stream will pass through the dust collection and/or mist removal apparatus unaffected.
Air treatment methods have been designed for vapor removal, such as removal of volatile organic compounds (VOCs) and the like. The problem with existing vapor removal methods is that these methods were developed primarily for chemical processes, and typically require a relatively clean air stream that is free of particulate contaminates. Note, for example, the vapor removal systems as shown in U.S. Pat. Nos. 4,820,318 and 5,089,033 and Gunderson, E. and Anderson, C., "Collection Device for Separating Airborne Vapor and Particulates", Am. Ind. Hyg. Assoc. J., 48(7); 634-638 (1987), which use a membrane or adsorption separation process to recover the condensable vapor component of the air stream. While this is very feasible in a chemical process, the particulate contaminants produced by a mechanical industrial process would quickly destroy any type of membrane or adsorption separation system. Other types of vapor removal systems, such as shown in U.S. Pat. Nos. 4,353,715, 4,986,836 and 5,123,936, use some type of particulate filter to cleanse the contaminated air stream before attempting to remove any vapor components. While this is feasible for air that is only mildly contaminated with particulates, such filter systems are quickly plugged in the dirty environments typically associated with most mechanical industrial processes. Still other types of vapor removal systems, such as shown in U.S. Pat. Nos. 4,863,495, 5,078,758, 5,085,673, 5,102,433, 5,108,469 and 5,122,165, attempt to remove vapors by combining the contaminated air stream with an aqueous mixture and then removing the resulting liquid. While this process is useful in certain situations, the process can be expensive and complicated, and adds significant amounts of liquids to the contaminant removal system, which must also be decontaminated.
While existing air cleaning methods are well-suited for removing mist and/or smoke, or for removing vapor, from a contaminated air stream generated by a mechanical industrial process, there is a need for an air cleaning method which can effectively dean a contaminated air stream that includes a heterogenous multi-component mixed density fluid (e.g., mist, vapor and/or smoke) such as the contaminated air streams generated by many mechanical industrial processes. It would also be advantageous to provide an air cleaning method which relied on an operational theory that takes into account a more accurate model of the complex behavior of contaminated air streams that comprise a haterogenous multi-component mixed density fluid.